Composition And Method For Removing Photoresist And Bottom Anti-Reflective Coating For A Semiconductor Substrate

ABSTRACT

A composition for removing photoresist and bottom anti-reflective coating from a semiconductor substrate is disclosed. The composition may comprise a nontoxic solvent, the nontoxic solvent having a flash point above 80 degrees Celsius and being capable of dissolving acrylic polymer and phenolic polymer. The composition may further comprise Tetramethylammonium Hydroxide (TMAH) mixed with the nontoxic solvent.

CROSS-REFERENCE TO RELATED APPLICATIONS

Noon This application is a divisional and claims priority to U.S. patentapplication Ser. No. 12/970,421, filed 16 Dec. 2010, which is entirelyincorporated by reference herein for all purposes.

TECHNICAL FIELD

The present invention relates to the field of resist-removing solutionsand particularly to a composition and method for removing photoresistand bottom anti-reflective coating for a semiconductor substrate.

BACKGROUND

Semiconductor device fabrication is the process used to createintegrated circuits that are present in electrical and electronicdevices. The fabrication process includes a sequence of photographic andchemical processing steps during which electronic circuits are graduallycreated on a substrate made of semiconductor materials. A typicalsubstrate is made out of silicon, and is sliced and polished to obtain aregular and flat surface.

Once the substrate is prepared, many process steps are necessary toproduce the desired semiconductor integrated circuit. Such steps can begrouped into two major parts: Front End of Line (FEOL) processing andBack End of Line (BEOL) processing. FEOL processing refers to theformation of the transistors directly in the silicon. In FEOLprocessing, a semiconductor substrate is developed by the growth of anultrapure, virtually defect-free silicon layer through epitaxy.Additional steps performed in the FEOL process include: growth of thegate dielectric (traditionally silicon dioxide), patterning of the gate,patterning of the source and drain regions, and subsequent implantationor diffusion of dopants to obtain the desired complementary electricalproperties.

Patterning refers to a series of steps that form or alter the existingshape of the deposited materials on the substrate. During patterning,the substrate is coated with a layer of photoresist. The photoresist isthen exposed to a pattern of intense light, and the areas of thephotoresist that are exposed to the intense light become soluble in adeveloper solution. A layer of anti-reflective coating may be utilizedto reduce reflections during the exposure. The anti-reflective coatingmay be located at the bottom of the photoresist, and may be referred toas the bottom anti-reflective coating (BARC) layer. After the exposure,the developer solution is utilized to remove the exposed photoresist,and the remaining photoresist is solidified to form a protection for theunderlying substrate during etching.

Etching refers to a step of utilizing chemical agents to remove theuppermost layer of the substrate in the areas that are not protected bythe remaining photoresist. Upon completion of the etching process, theremaining photoresist and anti-reflective coating are no longer neededand must be removed from the substrate. The photoresist may be removedutilizing plasma ashing, in which a plasma containing oxygen is used tooxidize the photoresist. Deionized (DI) water may be used subsequentlyfor DI water cleaning. However, plasma ashing processes may damagerefractory gate metals such as TiN, TaN and high-k dielectrics such asHfO₂ or HfSiO_(x). Furthermore, removal of the photoresist may bedifficult in areas that have been exposed to electron beam (ebeam)bombardment as a result of polymer cross-linking (e.g., if the substratehas been exposed to a post-lithography critical dimension scanningelectron microscopy (CDSEM) metrology step and has been exposed tolocalized areas of ebeam dosing).

Alternatively, a liquid photoresist removing solvent may be utilized tochemically alter the photoresist so that it no longer adheres to thesubstrate. Such removal processes are referred to as wet processes.However, a requirement for a reduction in the environmental safety andhealth (ESH) impact of such solvents has changed. For instance,N-methyl-pyrrolidone (NMP), solvent used in photoresist and BARCremoval, could be classified as reprotoxic.

BRIEF DESCRIPTION OF THE DRAWINGS

The numerous advantages of the present invention may be betterunderstood by those skilled in the art by reference to the accompanyingfigures in which:

FIG. 1 is a flow diagram illustrating a method for removing photoresistand BARC in a front end of line process; and

FIG. 2 is a block diagram illustrating a composition including anorganic and nontoxic solvent and Tetramethylammonium Hydroxide (TMAH).

DETAILED DESCRIPTION

Reference will now be made in detail to the presently preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings.

The present disclosure is directed to a composition and method forremoving photoresist and BARC in a front end of line process. A nontoxiccomposition and a wet process is disclosed that is capable of removingboth photoresist and BARC from a semiconductor substrate withoutdamaging the refractory gate metals such as TiN, TaN and high-kdielectrics. In addition, the composition and the wet process arecapable of removing both photoresist and BARC on the substrate in arelatively short amount of time.

FIG. 1 shows a flow diagram illustrating steps performed by a method 100for removing photoresist and BARC from a semiconductor substrate in afront end of line process. Step 102 may receive the substrate withphotoresist and/or BARC that need to be removed. Step 104 may apply acomposition to the substrate to dissolve the photoresist and BARC withinapproximately 1 minute or less. The substrate may be removed from thecomposition in step 106 once the photoresist and BARC are removed.

Referring to FIG. 2, an illustration depicting the composition 200 ofthe present disclosure is shown. The composition 200 includes a blend oforganic solvents 202 that has an appropriate concentration of a strongbase 204 and/or an oxidant. The solvent blend may dissolve photoresistand BARC within approximately 1 minute or less without attackingrefractory metal or a high-k oxide of a semiconductor. Furthermore, asolvent blend with short process time also means that a single wafer wettool may be utilized for resists removals.

The composition 200 is also capable of removing electron beam (ebeam)hardened resist for areas of the semiconductor that may have beenexposed to ebeams as a result of polymer cross-linking. For example, thesemiconductor substrate may be exposed to a post-lithography criticaldimension scanning electron microscopy (CDSEM) metrology, which mayexpose the substrate to localized areas of electron beams and harden thephotoresist that remains on the substrate. The ebeam hardenedphotoresist may be difficult to remove utilizing plasma ashing. However,the composition 200 of the present disclosure is capable of removingebeam hardened photoresist efficiently.

In one embodiment, the materials (chemical formulations) of solvent 202may be selected based on their Hansen Solubility parameters. Theselected materials may be nontoxic (e.g., based on ESH criteria), havinghigh flash points (e.g., above 80 degrees Celsius) and capable ofdissolving both acrylic polymer and phenolic polymer. In addition, theselected materials for solvent 202 may be selected based on theirefficiencies in dissolving photoresist materials such as ultravioletphotoresist. Furthermore, the selected materials for solvent 202 mayhave high polarity and may be required to mix well with water. Forinstance, a suitable material for solvent 202 may beN-(2-Hydroxyethyl)-2-Pyrrolidone (NHEP), Diethylene Glycol MonomethylEther (DEGME), or Dimethyl Sulfoxide (DMSO).

Base 204 may be added to the solvent 202 for BARC removal. The mixtureof the solvent 202 and the base 204 may produce a composition 200 havinga pH less than approximately 9. In one embodiment, TetramethylammoniumHydroxide (TMAH) is utilized as the base 204. The concentration of TMAHin the composition 200 is specifically blended so that the composition200 does not attack the refractory metal such as TiN and TaN or the highk material such as HfO_(x) or HfSiO_(x) during the resist-removalprocess.

TMAH is a quaternary ammonium salt with the molecular formula (CH₃)₄NOH.It is a phase transfer catalysis that facilitates acceleration of thereaction from one phase into another phase where reaction occurs. In thepresence of TMAH, ionic reactants are easily soluble in the organicsolvent 202. The amount and concentration of TMAH may be optimized toselectively etch BARC layer but not over-etch the gate metals such asTiN, TaN and high-k dielectrics such as HfO_(x) or HfSiO_(x).

For instance, if NHEP is utilized as the solvent 202, then the additionof TMAH to NHEP produces a composition 200 (having a concentration ofapproximately 2.5% of TMAH by volume) that may allow the composition 200to dissolve both photoresist and BARC on the semiconductor within 1minute or less. In another example, if DEGME is utilized as the organicsolvent, then the addition of TMAH to DEGME produces another composition200 (having a concentration of no more than approximately 2.5% of TMAHby volume) that may dissolve both photoresist and BARC on thesemiconductor within 1 minute or less at the temperature ofapproximately 50 degrees Celsius. In still another example, if DMSO isutilized as the organic solvent, then the addition of TMAH to DMSOproduces still another composition 200 (having a concentration of nomore than approximately 2.5% of TMAH by volume) that may dissolve bothphotoresist and BARC on the semiconductor within approximately 1 minuteor less at the temperature of approximately 60 degrees Celsius.

The effectiveness and the optimal chemical formulations of thecomposition of the present disclosure may be tested and determinedutilizing a high throughput approach. To reduce the number of substratesused for testing and product development, the etch rates of all thefilms of interest may be tested on blanket substrates by varying theprocess condition. This may include testing the etch rates onphotoresist, BARC, the underlying refractory material, and the high-k.The composition being tested may include various types of solvent andformulations mixed with different concentrations of base (TMAH). Inaddition, the tests may be conducted under different testing conditions,such as varying temperatures and varying agitation to the compositionfluid (e.g. stirrer speed). In one embodiment, a high productivitycombinatorial (HPC) system may be utilized to quickly generate a set oflibraries for the various compositions being tested. An exemplary HPCsystem is disclosed in: Combinatorial Process System, U.S. patentapplication Ser. No. 12/027,980, which is herein incorporated byreference in its entirety. Furthermore, the effectiveness of removingebeam or CDSEM hardened photoresist utilizing the composition of thepresent disclosure is also tested. For example, the CDSEM hardenedphotoresist may be reproduced for testing purposes utilizing a flood gundose that matches the CDSEM dose on a real product substrate.

It is believed that the present invention and many of its attendantadvantages will be understood by the foregoing description. It is alsobelieved that it will be apparent that various changes may be made inthe form, construction and arrangement of the components thereof withoutdeparting from the scope and spirit of the invention or withoutsacrificing all of its material advantages. The form herein beforedescribed being merely an explanatory embodiment thereof, it is theintention of the following claims to encompass and include such changes.

What is claimed is:
 1. A composition, comprising: a nontoxic solvent;and Tetramethylammonium Hydroxide (TMAH) mixed with the nontoxicsolvent; wherein the nontoxic solvent has a flash point above 80 degreesCelsius; and wherein the nontoxic solvent is capable of dissolvingacrylic polymer and phenolic polymer.
 2. The composition of claim 1,wherein the relative concentrations of the TMAH and the nontoxic solventresult in a pH less than approximately
 9. 3. The composition of claim 1,wherein the nontoxic solvent is capable of dissolving acrylic polymerand phenolic polymer in about 1 minute at a temperature between about 20and about 80 C.
 4. The composition of claim 1, wherein the concentrationof the TMAH is selected to not attack refractory metals exposed to thenontoxic solvent for less than about 1 minute.
 5. The composition ofclaim 1, wherein the nontoxic solvent has high polarity and mixes wellwith water.
 6. The composition of claim 1, wherein the nontoxic solventis N-(2-Hydroxyethyl)-2-Pyrrolidone.
 7. The composition of claim 6,wherein the TMAH mixed with the nontoxic solvent provides thecomposition a concentration of approximately 2.5% of TMAH by volume. 8.The composition of claim 1, wherein the nontoxic solvent is DiethyleneGlycol Monomethyl Ether.
 9. The composition of claim 8, wherein the TMAHmixed with the nontoxic solvent provides the composition a concentrationof no more than approximately 2.5% of TMAH by volume.
 10. Thecomposition of claim 1, wherein the nontoxic solvent is DimethylSulfoxide.
 11. The composition of claim 10, wherein the TMAH mixed withthe nontoxic solvent provides the composition a concentration of no morethan approximately 2.5% of TMAH by volume.
 12. A composition,comprising: an organic solvent capable of dissolving acrylic polymer andphenolic polymer; and Tetramethylammonium Hydroxide (TMAH) mixed withthe organic solvent.
 13. The composition of claim 12, wherein theorganic solvent is N-(2-Hydroxyethyl)-2-Pyrrolidone.
 14. The compositionof claim 13, wherein the TMAH mixed with the organic solvent providesthe composition a concentration of approximately 2.5% of TMAH by volume.15. The composition of claim 12, wherein the organic solvent isDiethylene Glycol Monomethyl Ether.
 16. The composition of claim 15,wherein the TMAH mixed with the organic solvent provides the compositiona concentration of no more than approximately 2.5% of TMAH by volume.17. The composition of claim 12, wherein the organic solvent is DimethylSulfoxide.
 18. The composition of claim 17, wherein the TMAH mixed withthe organic solvent provides the composition a concentration of no morethan approximately 2.5% of TMAH by volume.
 19. The composition of claim12, wherein the TMAH mixed with the organic solvent provides thecomposition a pH less than about
 9. 20. The composition of claim 12,wherein an amount and concentration of the TMAH is optimized toselectively etch a bottom anti-reflective coating (BARC) but not toover-etch a gate metal or a high-k dielectric.